"Most of them, I couldn't tell you if they're Republican or Democrat, and I don't care," Slay said. "Because, this is about doing the right thing for our communities, for our environment and for our economy."

From the headwaters in Minnesota to the Mississippi Delta, more than 18 million people get their drinking water from the main stem of the river, according to the group. Even though the waterway is one big economic engine, the mayors also pledged to make sure conservationists have a seat at the table as they move forward.

East St. Louis Mayor Alvin Parks said ensuring his community is adequately protected from flooding is a key part of his participation in the effort.

"Our infrastructure must be fool proof," Parks said. "We've got have that situation where it's at least 100-year-flood-proof, and preferably moving toward 500-year-flood-proof."